Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Coating – specific composition or characteristic
Patent
1980-07-03
1983-10-11
Powell, Jr., Everette A.
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Coating, specific composition or characteristic
415214, F01D 534
Patent
active
044089597
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a ceramic turbine wheel, expecially a ceramic radial turbine wheel for an exhaust gas driven turbine of a turbocharger for motor vehicles, with a body which is formed in one piece with radial blades and a hub which is connectable to a usually metallic turbine shaft.
BACKGROUND ART
With turbochargers for combustion engines in a power range suitable for motor vehicles, the turbine driving the compressor is fed by the exhaust gas of the combustion engine and to date has usually been constructed out of metallic alloys having high strength at high temperatures.
With reference to the increasing use of turbochargers in automobiles, an increased high temperature strength and an improved behavior of acceleration is desired. These requirements could be fulfilled by the use of ceramic materials in the turbocharger turbine. Ceramic materials, such as silicon nitride or silicon carbide, have a nearly constant high strength in the range of temperature under consideration, and have a density which is only one-third of that of a metallic material.
Due to the high temperature strength of such materials, the operating temperatures can be raised without danger, while the mass moment of inertia, due to the relative low density of the ceramic turbocharger rotor, can be reduced to about 40% of the moment of inertia of a metallic type rotor, and therefore, the time of response of the turbocharger correspondingly improves.
The experiments to develop such turbine wheels out of ceramic materials have up to now not yet led to the desired success, as there have resulted difficulties in the production process of the wheel, as well as other problems. Inadmissable defects to the components were found in the preferred, low-cost process, in which the radial turbine wheels, produced out of the ceramic material, are first of all fabricated as so-called green parts by injection molding or slip-casting techniques and afterwards subjected to a burn-out procedure for the binder followed by sintering or nitriding procedures. These defects are mainly attributed to a prevented escape of the gases produced by the burn-out of the binder as well as by a non-uniform shrinkage of the wheel with the solid body of the hub. A central, hollow bore, which would be favorable for the production process, is however not realizable for strength reasons, as by that shape the tensions resulting in operation would be increased to double the value of a hub without a bore.
The object of this invention is therefore construction of a ceramic turbine wheel, which, although it has a sufficient high temperature strength, does not show the above described difficulties in production.
DISCLOSURE OF INVENTION
This invention, accordingly, provides a ceramic turbine wheel, comprising: body portion; and about the axis, and connectable with a turbine shaft; core, on the side of the body portion opposite the hub portion.
By providing the body portion with a hollow central core, gases can emerge from the burn-out of the binder and escape out of the body, so that the formation of flaws is largely prevented.
In addition, according to this invention, the portion of the turbine from which the blades extend outwardly, will become more elastic, so that deformations of the blades can be taken up sooner without damage.
A radial turbine wheel, designed according to this invention, is producible without large difficulties by inexpensive production processes like injection molding or slip casting out of ceramic materials, e.g. silicon nitride and silicon carbide, wherein particularly the before mentioned difficulties in the necessary procedures of burn-out of the binders as well as in sintering and nitriding are prevented.
Especially with the material alpha silicon carbide, which shows in the mentioned production processes under high temperatures a large shrinkage, this design enables production with substantially reduced difficulties. See U.S. Pat. Nos. 4,124,667 and 4,144,207, regarding sintering and injection molding of alpha silicon carbide.
REFERENCES:
patent: 2297508 (1942-09-01), Schutte
patent: 3664766 (1972-05-01), Rahnke
patent: 3666302 (1972-05-01), Kellett
patent: 3801226 (1974-04-01), Bevan et al.
patent: 3897171 (1975-07-01), Stahl
patent: 4063850 (1977-12-01), Hueber et al.
patent: 4175911 (1979-11-01), Tiefenbacher
patent: 4295791 (1981-10-01), Johnson
Long William D.
Rottenkolber Paul J.
Green Raymond W.
Kennecott Corporation
Powell Jr. Everette A.
Sahr R. Lawrence
Volkswagenwerk Aktiengesellschaft
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